This invention relates to relatively narrow band antennas used with hand-held communications equipment. The invention is more specifically directed to such antennas which are disposed within the housing of the hand-held communications equipment.
Portable two-way radios have utilized a variety of antennas. One of the more common antennas used for such applications is a monopole. The use of a telescoping monopole is convenient since it can be retracted when not in use.
Antennas which are located within the housing of the portable communications equipment (subsequently referred to as an internal antenna) are desirable from the user's perspective. It eliminates a projecting external antenna which is subject to damage and may make a hand-held radio awkward to handle. Because of size limitations, internal antennas are often shorter than external antennas for the same frequency and have a narrower bandwidth.
When a conventional single input internal antenna is required to operate at two widely-separated frequencies such as for separate transmit and receive frequencies, a matching circuit has been used in order to provide a reasonable impedance match at both frequencies. For example, U.S. Pat. No. 4,571,595, entitled DUAL BAND TRANSCEIVER ANTENNA (corresponding to Ser. No. 558,270) provides a matching circuit in order to cover two separated frequency bands.
A conventional two-way radio having separate transmit and receive frequencies utilizes a duplexer circuit which serves to simultaneously couple the transmitter output and the receiver input to a common antenna. The duplexer serves to isolate the transmitter and receiver from each other.
Portable radios typically have antennas which are polarized along the long axis of the radio housing. These antennas provide optimum performance when the unit is held in the upright (vertical) position, such as when the user is holding the radio in front of his face and speaking into the microphone. However, fully duplex radiotelephones are not normally held in this optimum vertical position. Radiotelephones, like any telephone, are typically held in a nearly-horizontal position between the user's ear and mouth. This "telephone operating position" (i.e. tipped back 45 to 90 degrees to the vertical--typically 60 degrees) significantly degrades the portable radio antenna performance.
A need, therefore, exists for a portable radiotelephone antenna which provides improved performance when the radiotelephone is held next to the user's ear at an angle of approximately 30 degrees to the horizontal.